1. Field of the Invention
The present invention relates to a disk drive for floppy disks and more particularly to a disk drive having an alignment circuit that allows read/write head parameters, such as the radial alignment, track zero offset, index to data timing, write current level, asymmetry and threshold dropout to be electronically adjusted.
2. Description of the Prior Art
FIG. 1 shows a standard, commercially available disk drive 10 for use with a floppy disk 14, such as a double sided, high density, 96 track per inch (TPI), 5.25 inch diskette. A plurality of concentric magnetic data tracks data 16 are recorded on the disk 14. A pitch "P" is the distance separating adjacent data tracks. The disk drive 10 includes read/write carriage assembly 18 that supports an upper read/write transducer 22 (and a lower read/write transducer 24 which is not shown in FIG. 1) and moves on a pair of carriage guide rods 26. A shaft 30 of a stepper motor 34 is attached to the carriage assembly 18 by a band 38 to provide a means for moving the carriage assembly 18 in discrete steps. A read/write circuit 50 contains the electronic circuitry for enabling the transducers 22 and 24 to read and write data on the disk 14. A spindle motor 42 rotates the disk 14 under the transducer 22 during operation.
An index sensor 46 is positioned on the spindle motor for detecting when an index hole 50 in the disk 14 passes the sensor 46. Similarly, an optical track zero sensor 54 is positioned on the disk drive 10 for sensing when a flag 58 on the carriage assembly 18 passes the sensor 54.
In order for the disk drive 10 to function properly, it is important that the read/write transducer (head) 22 be properly aligned with respect to the data tracks 16 on the floppy disk. If the transducer 22 is not properly aligned, numerous problems arise in attempting to read and/or write data on the disk 14. Typical parameters that need to be kept within alignment specifications are the radial alignment, the track zero offset and the index to data offset. Additionally, parameters such as azimuthal alignment, write current and asymmetry are frequently monitored on an "end of life" basis (i.e. when these parameters fall sufficiently out of specification, the transducer 22 must be replaced).
With high volume industrial disk drives (e.g. disk drives used to record tens of thousands of copies of an applications program), it is not unusual for the disk drive to require alignment on a daily basis. Typically, the alignment procedure must be performed by a skilled technician. Even a simple alignment procedure can require fifteen to thirty minutes of the technician's time.
In a typical alignment procedure, a floppy disk having diagnostic information recorded on it (an alignment disk) is used to display an alignment signal indicative of the alignment status of the read/write transducer 22 on an oscilloscope or drive exerciser. Screws on the disk drive 10 are then loosened, the relevant part is manually moved to bring the parameter being displayed into specification, and the screws are then retightened to secure the part in a new position. For example, to set the radial alignment, the stepper motor 34 is manually moved and secured in a new position. To adjust the track zero alignment, the track zero sensor 54 is manually moved and secured in a new position. To adjust the index to data offset, the index sensor 46 is manually moved and secured in a new position. Write current and asymmetry are generally set during the drive manufacturing process using a procedure that involves manually adjusting a potentiometer that sets the write current and asymmetry. Once this adjustment is made, it cannot be readily changed.
In addition to requiring a skilled technician and being time consuming, a further problem with these manual adjustments is that the process of tightening the screws on the adjusted part often changes the position of the part and pushes the parameter back out of specification.
The alignment disks for accomplishing the manual alignment procedure are well-known. For example, U.S. Pat. No. 4,513,331, issued to Baker et al. on Apr. 23, 1985, shows a diagnostic diskette having prerecorded diagnostic tracks for providing reference data about various electrical and mechanical response characteristics of a disk drive. Other patents dealing with alignment diskettes include U.S. Pat. No. 4,748,524 (Fukaya et al., May 31, 1988); U.S. Pat. No. 4,513,333 (Young et al., Apr. 23, 1985); U.S. Pat. No. 4,608,618 (R. Sturtevant-Stuart, Aug. 26, 1986); U.S. Pat. No. 4,562,494 (C. Bond, Dec. 31, 1985); and U.S. Pat. No. 4,694,359 (T. Oya, Sep. 15, 1987).
Devices for analyzing the signals generated by the diagnostic diskettes are also known in the art. For example, Tronix, Inc. of Santa Clara, Calif., sells a Digital Media Analyzer (DMA) suitable for this purpose. U.S. Pat. No. 4,641,207, issued to Green et al. on Feb. 3, 1987, discloses an external diagnostic device that is coupled to the input and output terminates of a disk drive and monitors and/or generates signals used in checking various drive parameters such as track 00 (track zero) alignment, radial and azimuthal alignment of the read/write head, sector burst interval and disk speed. U.S. Pat. No. 4,754,343, issued to Cascio, Sr. et al. on Jun. 28, 1988, discloses a portable alignment device that displays a signal from an alignment disk in a manner that allows the stepper motor or head carriage assembly to be moved until the signal is optimized. U.S. Pat. No. 4,103,338, issued to Cizmic et al. on Jul. 25, 1978, discloses a disk drive exerciser having a memory for storing diagnostic programs. U.S. Pat. No. 4,321,636, issued to C. Lenz on Mar. 23, 1982, discloses a detector for using cat-eye type alignment tracks for aligning a read/write transducer.
Patents disclosing automated methods and devices for disk drive diagnostics are also known. For example, U.S. Pat. No. 4,935,835, issued to Godwin et al. on Jun. 19, 1990, discloses a method for using a special reference track on a floppy disk having optical servo tracks to automatically adjust the radial alignment of the read/write head and position the head relative to track zero U.S. Pat. No. 4,103,338, issued to Cizmic et al. on Jul. 25, 1978 discloses an apparatus for storing self-diagnostic programs for a disk drive. U.S. Pat. No. 4,149,199, issued to Chick et al. on Apr. 10, 1979, discloses a device for storing track eccentricity data for use in correcting the position of a read/write transducer. U.S. Pat. No. 4,825,313, issued to Moribe et al. on Apr. 25, 1989 discloses a method for using stored displacement values to correct the position of a magnetic head. British patent application GB 2226179-A, of Kani et al., published on Jun. 20, 1990, discloses a method and apparatus for verifying tracking errors that utilizes a stepper motor and an alignment disk.
Other patents disclosing disk drive diagnostic devices include U.S. Pat. No. 4,725,968, issued to Baldwin et al. on Feb. 16, 1988; British patent application GB 2225150-A, of Kanal et al., published on May 23, 1990; British patent application GB 2187878-A, of Kanai et al., published on Sep. 16, 1987. Japanese patent JP 62-287414, issued Dec. 14, 1987 to Ishida et al.; Japanese patent JP 63-201909, issued Aug. 22, 1988 to N. Adachi; Japanese patent JP 01-185893, issued Jul. 25, 1989 to C. Kawakami; and Japanese patent JP 01-159875, issued Jun. 22, 1989 to Mizunuma et al.